Coatings of glasses, glass ceramics or ceramics with organic materials are known according to the prior art. These coatings are designated as thick or thin layers. The thin layers have thicknesses of nanometer dimension to micrometer dimension. The proportion of substance of these organic coating components in comparison to the substrate material ranges from 0.2 mass % to about 5 mass %. Typical examples of such thin coatings are the simple application to glass fibers, the application of sol-gel layers to glasses (Schmidt, H., J. Non-Cryst. Sol. 178, 1994, 302) or the application of molding aids to ceramic powders for the production of high-strength ceramics, e.g. ZrO2.
Thin coatings of monolithic bodies consisting of metal or ceramic are presented by Tossatti et al. (Langmuir, 18, 2002, 3537). These coatings are biocompatible organic components which have, for example, a particular blood compatibility and have been applied to Ti metal or TiO2. Coating of powders is not mentioned.
On the other hand, it is known of dental powders which [lacuna] for the coating of substrates, e.g. of metal structures (e.g. of a dental crown, or of a multiple-membered bridge) or the coating of metal-free restorations, e.g. of glass ceramic (dental crown or three-membered bridge) for the optimal processing of the powders that mixing fluids have to be used in order to produce highly viscous or viscous slips. These mixing fluids allow the dental technician to produce a slip having optimal consistency from the dental powder. Thus the dental technician is able to apply the material to the suprastructure (e.g. crown, or bridge) using a brush and ideally to model the shape of the crown or bridge using this application process. The excess liquid is aspirated or removed using a hot air dryer. Subsequently, the next layer of slip is applied. The mixing fluids are aqueous media containing small amounts of organic and inorganic components.
After this coating process of the substrate with slip and initial removal of the liquid, the subsequent heat treatment is carried out from room temperature up to the termination of the sintering process, which is typically between 700° C. and 1000° C. Despite the use of mixing fluids, at various times situations occur where the dental powder does not adhere optimally to the substrate during the heat treatment, such that an optimal jointing process between dental powder and the substrate is not achieved in the finished product. This is visible in that, preferably in the approximal region of a crown or in the interdental region between individual crown segments of a multiple-membered bridge, a tearing or a lifting of the dental ceramic from the substrate is observed. If a situation of this type occurs, the dental technician has to apply an additional layer of slip in order to fill this resulting gap.
On the other hand, it is known of pulverulent dental ceramics, dental glass ceramics or dental glasses that during the shrinkage operation in the process of tightly sintering, uncontrolled reactions can occur, which alter the desired geometry (“distortion of a molded part”).
In DE 195 08 586 A1, the use of particles as a filler in filling composites which consist of an SiO2 core and are coated with another oxide is described. The focal point in the specification is the production of composites having specific X-ray opaque properties and an adjustable translucency. The possible subsequent coating of these “two-layer” SiO2 particles with an organic layer serves for the improved incorporation of these fillers into the organic matrix of the filling composite.
DE 197 41 286 A1 describes spherical particles which consist of an SiO2 core and/or further oxides and have a specific order of magnitude. In addition, these are coated with a polymerizable binder, this coating making possible covalent bonding of these particles to the polymer matrix and in this way guaranteeing a high strength of the organic/inorganic compound system in the composite.
US 2004/0224087 A1 describes the preparation and use of mixed oxide particles which consist of a number of layers of different oxides as fillers in dental composites, where one of the outer layers of the particles is essentially constructed of SiO2. The oxides of the core of the particles are constructed from various metals and have a higher refractive index than SiO2 alone.
US 2004/0134230 A1 also describes the preparation of fillers for composites. These glass powders have specific chemical properties and morphologies. In one case, these particles are also coated with organic materials, where the object of this coating is the better binding of these particles to the resin matrix.
EP 1 101 484 A2 describes fillers for dental composites. The fillers are not suitable for veneers of dental structures.
The particles described in DE 30 34 374 A1 are incorporated into dental composites as fillers. This coating consists of curable (polymerizable) plastics, preferably those from the organic matrix of the dental material. These coated particles are not employable as a glassy or glass ceramic veneer for dental restoration.
U.S. Pat. No. 4,412,015 relates to fillers for dental materials primarily based on barium fluorosilicate glasses or zeolites. The coating of the particles with the curable organic compounds serves exclusively for the increased strength of the compound system between the inorganic particles and the polymer matrix.
In WO 98/51419, a particle core of a sintered ceramic is described which is surrounded by a second metal compound. This coating is capable of entering into a permanent bond with other metals. As a whole, these particles are to be assigned to the sintered metallurgical products and are not comparable with the glassy or glass ceramic particles (dental powders).
EP 1 250 895 A2 relates to a process for the production of dental ceramic molded parts using electrophoretic deposition of oxide ceramic particles on a dental technology model. The slip described is deposited electrophoretically on a model and the oxide ceramic green article thus obtained after a drying process is tightly sintered at temperatures between about 1100° C. and approximately 1700° C. Afterward, veneering is carried out in a manner known from the prior art.
U.S. Pat. No. 5,122,418 describes the preparation of a powder for cosmetic applications, certain properties of course also being predominant in this case.
In summary, it is to be observed that not one coating of the dental powder which has good and advantageous processing properties in the processing and heat treatment is described in the prior art mentioned.